This invention relates to a high voltage pulse generator of the Marx type, in which capacitors are charged in parallel and discharged in series.
Amongst the many techniques for producing high voltage pulses, the Marx generator is probably the best known and most widely used. For the combination of short risetime and low output impedance (i.e. high power), large energy, high efficiency and waveform flexibility--the Marx principle is peerless.
The essence of the Marx principle is to charge a number of capacitive storage elements (electrostatic energy stores) in parallel and then, through transient switching techniques, connect (or "erect") the elements in series, thus producing an effective multiplication of source voltage. And the key to the Marx operation lies in the triggering of the series-connecting switches. In the original generator described by Erwin Marx in 1923, the capacitors were charged in parallel through high resistances and the switches were simple, 2-electrode spark gaps triggered by the over-voltage accumulating from the switching of previous stages.
The state of the art is summarized by R. A. Fitch in the IEEE Transactions on Nuclear Science, Vol. NS-18, #4, pages 190-198 (August 1970). The greatest development in terms of waveform duration and flexibility has occurred within the last one or two decades. To this time, virtually all circuits have been limited to single-shot operation because of the limitations of spark gaps.
Next generation application of Marx Banks to power high energy lasers and electron beams will require circuits capable of repetitive operation ranging up to kilohertz (kHz) frequencies. This requirement poses severe difficulties for the spark gap as a Marx switching component. To obtain a low pre-fire probability on this device will require extraordinary research and development efforts, and likely produce circuits and configurations that are much less compact than their single-shot counterparts.
In response to the recognized need for a Marx generator capable of a high repetition rate, I have investigated Marx circuitry using modern thyratrons as the switching elements. Because of the relatively high voltage trigger requirements of spark gaps, Marx circuitry developed for these devices has concentrated on achieving a balance between hold-off reliability and triggering schemes that produce an orderly erection mode, so that predictable output pulses may be realized. High repetition rate capability, low voltage trigger requirements, and high reliability are well known thyratron characteristics when used in a conventional manner. However, particular problems arise with the use of thyratrons in a Marx circuit, such as both external and internal arcing, because of progressively increasing overvoltages.